They fell victim to vanity, thinking that they could establish a foundation that would further their philosophies and goals long after they were dead, that would not be captured by those with different philosophies
A conservative would be better served by having any foundation have a sunset clause, which would mandate that all the money be distributed to worthy conservative causes and individuals within 20 years, at which point the foundation terminates.
Actually, a conservative would be better off spending as much of the money as possible while alive according to their wishes. That way no smooth-talking lawyer can twist his/her intent at all.
The other necessary tactic is to so narrowly construct one’s will and trust(s) that no lawyer can “interpret” your foundation/trust to their ends.
The sunset clauses AND the narrow construction are what kept the Olin Foundation on track:
http://en.wikipedia.org/wiki/John_M._Olin_Foundation